1. Field of the Invention
Embodiments disclosed herein relate generally to apparatus and methods for controlling drilling fluid or “mud” pressure in a mud pump system. More specifically, embodiments disclosed herein relate to using a pressure limiting controller for controlling mud pressure.
2. Background Art
During a drilling operation, drilling fluid or “mud” is circulated through a mud pump system. Typically, mud flows down a drillstring to a rotating drill bit, which is suspended in a borehole. The mud flows through the drill bit by exiting through openings in the drill bit. As the mud exits, it flushes out drill cuttings generated by the drill bit. Then, the mud flows up an annular space between the drillstring and the sides of the borehole, carrying the drill cuttings to the surface.
Under normal operating conditions of the mud pump system, the factors affecting the hydraulic characteristics of the mud are fairly constant at a given depth. Depending on the working pressure requirement, the pumping rate of the mud pump is determined, and the mud pump is maintained at this constant rate. However, these hydraulic characteristics can suddenly change due to blockages in the drill bit. If the pumping rate is maintained the same as before, these blockages can cause a sudden surge in mud pressure.
Safety valves are currently used to relieve the system if the pressure surge exceeds the maximum allowable pressure. However, these safety valves present a limitation because when they open in response to a sudden pressure surge, the mud flow diverts back to the surface tanks, shutting down the drilling operation. Frequent shutdowns are undesirable. Furthermore, conventional pressure control systems are generally unstable and cannot accommodate various levels of blockage and operating conditions.